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A simple 'one-pot' approach for the preparation of a new vinyl-functionalized organic-inorganic hybrid monolithic column is described. In this improved method, the hydrolyzed alkoxysilanes of tetramethoxysilane and triethoxyvinylsilane were used as precursors for the synthesis of a silica-based monolith, while 1-hexadecene and sodium ethylenesulfonate were used as vinyl functional monomers along with azobisisobutyronitrile as an initiator. The effects of reaction temperature, urea content, and composition of organic monomers on the column properties (e.g. morphology, mechanical stability, and chromatographic performance) were investigated. The monolithic column was used for the separation of neutral solutes by reversed-phase pressurized capillary. Furthermore, the monolith can separate various aromatic amines, which indicated its excellent cation-exchange capability and hydrophobic interactions. The baseline separation of the aromatic amines was obtained with a column efficiency of up to 78 000 plates/m. [ABSTRACT FROM AUTHOR]

Abstract: A simple and rapid pressurized isocratic capillary electrochromatography (pCEC) method has been developed to separate six pyrethroid pesticides. The effects of pH of buffer, organic solvent content, buffer concentrations and applied voltage on the separation of six pyrethroids were investigated. Under the optimized conditions, the pCEC method developed allows baseline separation of a complex mixture of six pyrethroids in <20min. The method is applied to the analysis of these pesticide residues in Chinese cabbage. The limits of quantification (LOQ) ranged from 0.5 to 0.8μg/ml (corresponding to 0.05 and 0.08mg/kg in the vegetable sample), with relative standard deviations (R.S.D.) <5.0%. Mean values of recoveries for six pyrethroids ranged from 89.6 to 96.3%, respectively. [Copyright &y& Elsevier]

Abstract: In this paper, the pressurized capillary electrochromatography (pCEC) with UV detection was utilized for the separation and determination of three structurally related estrogens, such as diethylstilbestrol (DES), hexestrol (HEX) and dienestrol (DE), which were difficult to be separated by capillary electrophoresis (CE) and HPLC due to their similarity in the structure and charge-to-mass ratios. Experiments were carried out in a commercially available pCEC instrument using a capillary column packed with 3μm octadecyl silica (ODS). Surfactant sodium dodecyl sulfate (SDS) was introduced in the mobile phase to enhance the speed of analysis. The effective factors on the retention time and separation resolution, such as the applied voltage, supplementary pressure, the pH and the concentration of the buffer solution, the concentration of SDS, and the content of acetonitrile in the mobile phase, were evaluated. Based on the investigation, 31% (v/v) acetonitrile and 69% (v/v) of 10mmol/L phosphate buffer (pH 6.5) containing 1.0mmol/L SDS at an applied voltage of −12kV and a supplementary pressure of 1000psi were found to be the optimal conditions for pCEC to separate the three estrogens. The method also had been applied to the analysis of fish muscle samples spiked with estrogens. [Copyright &y& Elsevier]

Abstract: Molecularly imprinted monolithic columns were prepared for chiral separation of tyrosine and its amino acid derivatives by in situ therm-initiated copolymerization of methacrylic acid, 4-vinylpyridine and ethylene glycol dimethacrylate. The enantiomers were rapidly separated on monolithic columns in less than 10min by pressurized capillary electrochromatography (pCEC). The influences of several parameters such as the content of cross-linking monomer on the composition of the pre-polymerization mixture were systematically investigated. The influence of the pCEC conditions including the composition of the mobile phase was also optimized to obtain the good enantioseparation. It was found that in addition to molecularly imprinted recognition, chromatographic retention and electrophoretic migration play important roles in the retention and chiral recognition of molecularly imprinted polymer (MIP) columns. The cross-selectivity for similar amino acids and its derivatives were systematical investigated for understanding the recognition mechanism on the MIP monolithic columns. The results indicated that molecularly imprinted polymer recognizes the template molecule by its molecular shape defined binding cavity. [Copyright &y& Elsevier]

Abstract: A polar and neutral polymethacrylate-based monolithic column was evaluated as a hydrophilic interaction capillary electrochromatography (HI-CEC) stationary phase with small polar–neutral or charged solutes. The polar sites on the surface of the monolithic solid phase responsible for hydrophilic interactions were provided from the hydroxy and ester groups on the surface of the monolithic stationary phase. These polar functionalities also attract ions from the mobile phase and impart the monolithic solid phase with a given zeta potential to generate electro-osmotic flow (EOF). The monolith was prepared by in situ copolymerization of a neutral monomer 2-hydroxyethyl methacrylate (HEMA) and a polar cross-linker with hydroxy group, pentaerythritol triacrylate (PETA), in the presence of a binary porogenic solvent consisting cyclohexanol and dodecanol. A typical HI-CEC mechanism was observed on the neutral polar stationary phase for both neutral and charged analytes. The composition of the polymerization mixture was systematically altered and optimized by altering the amount of HEMA in the polymerization solution as well as the composition of the porogenic solvent. The monoliths were tested in the pCEC mode. The resulting monoliths had different characteristics of hydrophilicity, column permeability, and efficiency. The effects of pH, salt concentration, and organic solvent content on the EOF velocity and the separation of nucleic acids and nucleosides on the optimized monolithic column were investigated. The optimized monolithic column resulted in good separation and with greater than 140,000theoreticalplates/m for pCEC. [Copyright &y& Elsevier]

A novel strategy for rapidly fabricating ionic liquid (IL)-bonded multifunctional monolithic stationary phase has been developed by an in-situ polycondensation of urea-formaldehyde (UF) and a lab-made acylamino-functionalized IL (1-acetylamino-propyl-3-methylimidazolium bromide, [AAPMIm]Br). Two polycondensation processes of UF with 1-amino-propyl-3-methylimidazolium bromide or [AAPMIm]Br were evaluated. Several parameters including mass ratio of urea-formaldehyde, amount of [AAPMIm]Br, polycondensation time and reaction temperature were optimized, and the [AAPMIm]Br-bonded monolithic stationary phase could be rapidly synthesized in 10 min with a satisfactory permeability and mechanical stability. Used for pressurized capillary electrochromatography (pCEC), a typical hydrophilic interaction (HI) retention could be obtained in the resultant [AAPMIm]Br-bonded monolith when the content of acetonitrile (ACN) in mobile phase exceeded 20%. Multiple retention mechanisms such as hydrophilic interaction (HI), hydrogen bond (H H), anion-exchange and cation-exclude interactions, were acheived in the [AAPMIm]Br-bonded monolith. Various polar compounds including phenols, benzoic acid and its homologues, and enkephalins have been well separated and thus demonstrated a satisfactory separation performance of the obtained monolith. A facile access is lighted for rapid preparation of ionic liquid-bonded monoliths with multiple retention mechanisms for pCEC. [ABSTRACT FROM AUTHOR]

Highlights: [•] Novel vinylbenzyl quaternary ammonium-based monolith was fabricated. [•] Good mechanical stability, permeability and reproducibility were obtained. [•] Efficient separations were presented for various polar analytes. [ABSTRACT FROM AUTHOR]

Abstract: A novel organic-silica hybrid monolithic stationary phase with a mixed-mode of hydrophilic and strong anion-exchange interactions (HI-SAX) was prepared with a modified “one-pot” process of functional monomers and alkoxysilanes. Using a hydrosoluble initiator 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AIBA), the homogeneous prepolymerization system of this hybrid monolith was successfully obtained by a simple operation. The polycondensation of alkoxysilanes (tetramethoxysilane (TMOS) and vinyl-trimethoxysilane (VTMS)) and the in situ copolymerization of a quaternary ammonium group-containing acrylic monomer ([2-(acryloyloxy)ethyl] trimethyl ammonium methyl sulfate (AETA)) on the precondensed siloxanes were achieved. The morphologies of the hybrid-silica monolithic matrixes were observed by SEM, and the performances of the organic-silica hybrid monolithic columns were investigated by pressurized capillary electrochromatography. The mechanical stability and reproducibility of the obtained hybrid monolithic column preformed acceptable. Both hydrophilic interaction chromatography mechanism and strong anion-exchanged interaction were investigated. A mixed mode of HI-SAX was obtained for the analysis of nucleotides with a good resolution, and the separation of polar and basic nucleic acid bases and nucleosides was also achieved without peak tailing. [Copyright &y& Elsevier]

Abstract: A novel highly hydrophilic polymethacrylate-based monolithic stationary phase based on the copolymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and pentaerythritol triacrylate (PETA) was designed for pressurized capillary electrochromatography. A typical hydrophilic interaction chromatography mechanism could be observed when the content of acetonitrile (ACN) in the mobile phase exceeded 25%. Slight swelling or shrinking with mobile phases of different polarity was observed in permeability studies. Good retentions and efficient separations of polar analytes, such as neutral amides and phenols, were well achieved in hydrophilic interaction chromatography mode with only about 50% ACN content in the mobile phase. It was remarkably lower than the content of ACN (>90%) used on the hydrophilic polymethacrylate-based monoliths reported previously. Additionally, a mixed mode of hydrophilic interaction (HI) and strong cation-exchange (SCX) could be also obtained in the analysis of charged peptides, and high column efficiency up to 80,000plates/m was achieved without peak tailing. The prepared hydrophilic stationary phase might provide a potential environmental friendly separation media for polar solutes as it consumes a low volume of organic solvents. [Copyright &y& Elsevier]

Abstract: In this paper, pressurized capillary electrochromatography (pCEC) with laser induced fluorescence detection (LIF) was demonstrated as a viable approach for the separation and determination of trace flavins in human plasma, where flavins tend to be degraded ex vivo. Using a sulfonated N-octadecyl methacrylate monolithic column in isocratic pCEC separation, symmetrical peak shapes and rapid separation could be obtained in a weakly acidic mobile phase. Baseline separation of riboflavin, flavin mononucleotide and flavin adenine dinucleotide could be achieved within 4.5min in a mobile phase containing 60% (v/v) acetonitrile and 40% (v/v) of 20mmolL−1 phosphate buffer (pH 4.0), with −22kV of applied voltage and 290psi of supplementary pressure and 0.02mLmin−1 of flow rate. Based on a 473nm laser diode double pumped solid state source, flavins could be determined by LIF with the detection limit (LOD) as low as 0.5nmolL−1 (S/N=3). The concentration ranges were 0.005–2μmolL−1 for RF and FMN, and 0.02–40μmolL−1 for FAD. Owing to the weakly acidic condition selected in this experiment, the high fluorescence quantum yields and good stability of flavins contributed to a preferable analysis. Combined with a simple clean-up procedure, this method has been proved to be effective for the rapid and selective analysis of trace levels of flavins in human plasma without sample preconcentration. [ABSTRACT FROM AUTHOR]

Abstract: A monolithic stationary phase was prepared by in situ copolymerization of 2-hydroxyethyl methacrylate (HEMA), ethylene dimethacrylate (EDMA), and methacrylic acid (MAA), in a binary porogenic solvent consisting of toluene and 1-dodecanol. The resulting monolith was evaluated as a hydrophilic interaction-capillary electrochromatography (HI-CEC) stationary phase under the mode of pressurized capillary electrochromatography (pCEC). Effects of the buffer pH, salt concentration and the mobile phase composition on the electroosmotic flow (EOF) velocity and the retention factors of the compounds were investigated. The generation of cathodic EOF under a broad pH range was attributed to the presence of the carboxyl groups on the surface of the polar stationary phase. The carboxyl groups offered at the same time the possibility of weak electrostatic interaction with analytes. The separation mechanism of the monolithic column was discussed in detail. It was found that the separation mechanism of charged solutes could be attributed to a mixed mode of HI and weak electrostatic interaction, as well as the effect of electrophoresis, while the separation of neutral solutes was based on the hydrophilic interaction at high acetonitrile (ACN) content. [Copyright &y& Elsevier]

Abstract: A simple and convenient end-column chemiluminescence (CL) detection coupled to pressurized capillary electrochromatography (pCEC) was described. Luminol and N-(4-aminobutyl)-N-ethylisoluminol (ABEI) were adopted as mode compounds to evaluate the feasibility of end-column reactor. Detailed analysis of ABEI revealed that the high sensitivity could be obtained with the reactor. Furthermore, determination of norepinephrine (NE) and epinephrine (EP), which were labeled with ABEI, was accomplished by using the end-column pCEC–CL detection based on ABEI–potassium ferricyanide–alkaline medium CL reaction system. Under the optimum conditions, the detection limit (S/N=3) of NE and EP was 0.08μM and 0.06μM, respectively. The proposed method has also been successfully applied to the analysis of adrenaline hydrochloride injection sample. [Copyright &y& Elsevier]

Abstract: In this report, the preparation of porous polymethacrylate-based monolithic columns by in situ copolymerization of octadecyl methacrylate (OMA), 3-sulfopropyl methacrylate (SPMA) and ethylene dimethacrylate (EDMA) in a binary porogenic solvent consisting of cyclohexanol/1,4-butanediol are proposed. These monoliths possess in their structures bonded octadecyl ligands and sulfonate groups and are evaluated in pressurized capillary electrochromatography (pCEC) system using small neutral and charged solutes. While the sulfonate groups are meant to generate the electroosmotic flow (EOF) necessary for transporting the mobile phase through the monolithic capillary; the octadecyl ligands are introduced to provide the nonpolar sites for chromatographic retention for neutral solutes. However, incorporating the sulfonate groups in the monoliths does not only support the EOF but also exhibit hydrophilic interaction as well as electrostatic interaction/repulsion with the monoliths in addition to electrophoretic migration with polar charged solutes (e.g., nucleotides). The monolithic stationary phases at different EOF velocities are easily prepared by altering the amount of SPMA in the polymerization solution as well as the composition of the porogenic solvent. Optimum EOF velocity, the highest efficiency and adequate chromatographic retention are obtained when 0.6% SPMA is added to the reaction mixture. Under these conditions, rapid separation and high plate counts reaching greater than 170,000plates/m are readily obtained. [Copyright &y& Elsevier]

Abstract: A pressurized capillary electrochromatography (pCEC) with monolithic column has been developed for the rapid separation and determination of five structurally related anthraquinones in Rhubarb. The possibility of rapid separation resulted from the unique pore structure with high permeability and favorable mass transfer characteristics of the monolithic stationary phase. The effect factors such as organic modifier, acidity and concentration of running buffer, separation voltage were investigated to acquire the optimum condition. In the 220nm wavelengths, the five anthraquinones could be baseline-separated rapidly within 5min with the separation voltage of −20kV in 10mmol/L phosphate buffer (pH 6.2) containing 65% acetonitrile. The calibration graphs of rhein, aloe-emodin, emodin chrysophanol and physcion were linear by plotting the peak area against the analytes concentration over the range of 0.2–65, 0.1–30, 0.1–55, 0.5–30 and 0.5–55μg/mL, respectively. The detection limits of five anthraquinones were ranged from 0.06 to 0.2μg/mL and the recoveries of Rhubarb samples were about 81.3–86.4% (R.S.D.≤5.2%). This proposed method was successfully applied to determination of the five analytes in Rhubarb with satisfactory results. [Copyright &y& Elsevier]